Process of utilizing detergents to solubilize keratin materials



Patented Aug. 8, 1950 PROCESS OF UTILIZING DETERGENTS TO SOLUBILIZE KERATIN MATERIALS Chase B. Jones, Waltham, Mass., and Dale K. Mecham, Richmond, CaliL, assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application November 23, 1948, Serial No. 61,694

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 4 Claims.

This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented in any country, may be manufactured and used by or for the Government of the United States of America for governmental purposes throughout the world without the payment to us of any royalty thereon.

This application is a continuation-in-part of our copending application for patent, serial No.-

74B,849, filed May 8, 1947, now abandoned.

This invention relates to a method of dispersing keratin proteins obtained from a keratin ma.- terial, such as feathers, hoofs, horns, wool, and so forth, and has among its objects the use of such keratins, either in the dispersed or recovered forms, in the preparation of artificial fibers, films, plastics and the like.

Keratins, like themore soluble proteins, can be readily dispersed by hydrolysis in strong acids or alkalis, but the keratin thus dispersed cannot be recovered except as simple degradation products, such as amino acids or complex degradation products, such as peptides, peptones, and proteoses, the properties of which differ radically from those of the original keratin.

Keratins can also be dispersed in alkaline solutions of metallic sulphides and such sulphides are commonly used in cosmetic depilatories and in the removal of hair from hides in the tanning industry.

Keratins have also been dispersed at neutral reactions, but in these cases heat and high temperatures were employed to the point of charring, which produced drastic degradation oi the proteins.

Also, keratins may be dispersed in strong alkaline solutions by treatment with reducing agents, and the recovered protein is more similar to the original protein in regard to solubility, molecular size, and so forth, than are the peptides, proteoses, and so forth, referred to previously. However, the presence of the strong alkali is undesirable because it presents an opportunity for the hydrolysis of the keratin, destruction of the cystine constituent of the keratin (keratins being unique among proteins in that they contain exceptionally large amounts of cystine), and destruction of the hydroxy amino acid residues of the keratin.

According to our invention, keratin materials are dispersed under mild conditions, that is, in neutral or practically neutral reaction, and at relatively low temperatures. These conditions produce less degradation of the original keratin than occurred in the prior art and the dispersed keratin may be recovered in a form substantially similar to that of the original keratin in regard to its composition, lsoelectric point, solubility, and other properties.

The method involved in this invention is based partly on the reduction of the disulphide bonds within the keratin molecule by treating it with sulfur-containing, reductive disulphide-splitting agents, such as monoethylene thioglycol (thioglycol), thioglycolic acid (present as the thioglycolate in neutral solution) and sodium bisulphite.

The presence of alkali is obviated by the use of any of a number of protein-denaturing or protein-dispersing agents, such as urea, guanidine hydrochloride, ammonium thiocyanate, tormamide, acetamide, thiourea, sodium salicylate, urethane, phenol, lithium iodide, and surfaceactive agents, such as synthetic detergents composed of alkyl aryl sulfonates or alkyl sulphates and dispersion or the keratin is thus eflected at neutral or practically neutral reaction.

Theretore, under the above conditions of employing disulphide-splitting and protein-dispersing or protein-denaturing agents to efiect the dispersion in neutral or practically neutral reaction and at relatively low temperatures, the keratin molecule undergoes minimal degradation, the only chemical attack on the covalent linkages of the keratin being the cleavage or the disulphide bonds of the cystine moiety.

The following examples are illustrative of our invention:

EXAMPIE I ings are treated with this neutralized solution in,

a water bath at about 40 C. about :for 18 hours. The mixture is stirred at convenient intervals.

During this period about 74% ot the hoof kera- 3 tin is dispersed in the solution. After removal oi the undispersed hoof by filtration, the dispersed keratin may be precipitated either by dilution with several volumes of water, by salting out with M3804, (NHa) 2804. etc., by acidification, or by dialysis. If desired, the guanidine may be removed from the dispersion by dialysis and may be recovered from thedialysate by precipitation as the nitrate or by other suitable means.

EXAMPLE lI 1.1 parts of NaHSOa and 21 parts of urea are dissolved in water. Sodium hydroxide solution and water are added as required to obtain 35 parts of solution at about pH 7.1. 2.5 parts of wool are treated with this solution in a water bath at about 40 C. about for 18 hours, during which period the mixture isstirred at frequent intervals. 52% of the original weight of the wool is dispersed by this treatment. The dispersed wool may be precipitated and recovered from the solution either by dialysis, by salting out with M8504. (N114) 2804, etc., or by careful addition of a suitable amount of acid or alkali.

EXAMPLE III 40 parts of a synthetic detergent (a sodium alkyl benzene sulphonate'wherein the alkyl group contains 12 to 18 carbon atoms) and 4 parts of Hal-ISO: are dissolved in water. Sodium hydroxide solution and water are added as required to obtain 400 parts of solution at about pH 6.5

This solution is heated to boiling and 64' parts of I chicken feathers are added. The solution is kept boiling gently for about minutes with frequent stirring. During this period considerable dispersion of the feathers occurs and the undispersed portion becomes very soft and loses its original shape. 200 parts of boiling water are now added and the solution is boiled and stirred for about another 30 minutes. The undispersed residue is removed by suitable filtration and is washed several times in hot water. The washings and filtrate may be combined and evaporated to dryness to obtain 70 parts of a water-soluble product that has been found useful for the preparation of artificial fibers. This material contains 8.5% to 8.6% nitrogen on a dry basis.

EXAMPLE IV 50 parts of a synthetic detergent, composed of sodium dodecyl sulphate, and 10 parts of NaHSOa are dissolved in 940 parts of water. A saturated solution of sodium hydroxide is added until the pH of the solution is about 6.0. The solution is heated to boiling and 80 parts of chicken feathers are added. The solution is gently boiled for about one hour with frequent stirring. The undispersed residue is removed by suitable filtration and is washed several times in hot water. The combined washings and filtrate are evaporated to dryness. parts of dry product are obtained having a nitrogen content of 8.5% to 9.6%. This material has been found useful for the preparation of artificial fibers.

EXAMPLE v 1 1.6 parts of thioglycolic acid and 21 parts of urea are dissolved in water. Sodium hydroxide solution and water are added as required to obtain 35 parts of solution at about pH 7.0 (20.2). 2.5 parts of duck feathers are added, and the mixture is heated at about 40 C. about for 18 hours. About 78% of the feather keratin is dispersed by this treatment.

EXAMPLEVI 1.4 parts of monothioethylene glycol and 24 parts of ammonium thiocyanate are dissolved in water. Sodium hydroxide solution and water are added as required to obtain 35 parts of solution having a pH of about 6.9. 2.5 parts of chicken feathers are treated with this solution for about 18 hours at about 40 C. During this period about 82% of the feather keratin is dispersed.

EXAMPLE VII 1.4 parts of monothioethylene glycol and 20.7 parts of acetamide are dissolved in water. Sodium hydroxide solution and water are added to give 35 parts of solution having a pH of about 7.2. 2.5 parts of chicken feathers are treated with this solution at about 40 C. about for 18 hours. During this period about 59% of the feather keratin is dispersed.

EXAMPLE VIII other experiments were performed, the results of which are shown in the following tables:

TABLE I Dispersz'bz'lzties of keratins in difierent dispersing agents upon reduction by 0.5 M thioglycol [2.5 g. of keratin was treated for 18 hours at about 40 C. with 35 mi. 0! solution at pH 7.]

Guanidine S thetic l N H CNS Formamide Acetamlde Thlourea 3m Kent 5% 9.0 M) (10.0 M) (10.0 M) 1.2 M) 83 2? Per cent Per cent Per cent Per cent Per cent Per cent 2 Chicken feather 84 82 66 5 l 79, Due]: leather 83 80 41 36 6 51, 53 Tortoise scutes 84 52 10, 8 Snake skim" 55 44 26, 30v Cattle hooi 74 56 7 6 5 58, 64

l 61 36 4 6 4 44, 50 Cattle horn 36 27 3 5 4 14, 12' 0g hair 56 26 2 2 2 4, 3 Human a 50 ll 0 0 2 2, l v Ovokeratin 8 6 4 3 l5 2, 4

1 Composed of sodium dodecyl sulphate. 1 First values calculated from dry weights of residues after acetone extraction; second values calculated from nitrogen analyses.

TABLE II Dispersibilities of keratins in M urea upon reduction by difierent disulphide-splitting agents Many changes and variations in the conditions for dispersion shown in the foregoing examples and tables may be made. As a rule, the higher the concentration of protein-dispersing or protein-denaturing agent, the reater is the percentage of keratin dispersed, the solubility of the dispersing or denaturing agent being a limiting factor. A greater degree of dispersion may also be obtained in some cases by increasing the concentration of the disulphide-splitting agent, as for example, for monoethylene thioglycol and thloglycolic acid. An increase in the concentration of NaHSOs, however, often results in a decrease in the extent of dispersion of the keratin, presumably due to a salting-out efiect.

Also, it is not necessary in every case that the solution be near the point of neutrality (pH 7.0) For example, the dispersibility of human hair in a solution of thioglycol and sodium salicylate is increased as the pH of the solution is increased about from 6.9 to 11.4. The use of neutral solutions merely minimizes the possibility of hydrolytic degradation of the protein which may be detrimental in some cases. If the pH is increased above about pH 10, dispersion occurs if only a disulphide-splitting agent is present; however, the presence of a protein-dispersing or proteindenaturing agent, as used in our invention permits dispersion below pH 10.

The temperature at which dispersion, according to our invention, is obtained may range up to about 100 C., and the higher the temperature within this range, the shorter the time required for dispersion, and in some cases, a higher degree of dispersion is obtained. Therefore, it is recommended that the invention be conducted at a temperature range of up to about 100 C.

The detergents which may be used to disperse the protein may be any alkyl aryl sulphonate or alkyl sulphate which has detergent properties. The held of detergents has been developed thoroughly in the last years and almost innumerable series of alkyl aryl sulphonates and alkyl sulphates having detergent properties have been described and/or patented. It has been shown that it is esential that besides the sulphate or sulphonate group (the hydrophilic group) the compound must also contain a high-molecular weight hydrocarbon or other hydrophobic group. There must be a balance between these two opposed groups to give the compound the requisite detergent properties. Thus in the case of the alkyl sulphates and alkyl benzene sulphonates the alkyl radical must possess 8 to 18 carbon atoms. In the case of alkyl naphthalene sulphonates the suiting alkylated benzene.

alkyl group may contain less carbon atomsdown to. three are efiective. These detergents are generally employed in the form of their alkali metal salts-i. e., their potassium, sodium, or ammonium salts. Some or the particular detergents which we may use are sodium octyl benzene sulphonate, sodium nonyl benzene sulphonate, sodium decyl benzene sulphonate, sodium undecyl benzene sulphonate, sodium dodecyl benzene sulphonate, sodium tridecyl benzene sulphonate, sodium tetradecyl benzene sul phonate, sodium hexadecyl benzene sulphonate, sodium heptadecyl benzene sulphonate, sodium octadecyl benzene sulphonate, sodium tri (isopropyl) benzene sulphonate, sodium tetra (isopropyl) benzene sulphonate, sodium di (isobutyl) benzene sulphonate, sodium tri (isobutyl) benzene sulphonate, sodium tetra (isobutyl) benzene sulphonate, any of the above named compounds in the form of their potassium or ammonium salts, sodium isopropyl naphthalene sulphonate, sodium di (isopropyl) naphthalene sulphonate, sodium tri (isopropyl) naphthalene sulphonate, sodium isoamyl naphthalene sulphonate, sodium di (isoamyl) naphthalene sulphonate, sodium isobutyl naphthalene sulphonate, sodium di (isobutyl) naphthalene sulphonate, sodium tri (isobutyl) naphthalene sulphonate, sodium octyl naphthalene sulphonate, sodium decyl naphthalene sulphonate, or any of the above named alkyl naphthalene sulphonates in the form of their potassium or ammonium salts, sodium octyl sulphate, sodium nonyl sulphate, sodium decyl sulphate, sodium undecyl sulphate, sodium dodecyl sulphate, sodium tridecyl sulphate, sodium tetradecyl sulphate, sodium pentadecyl sulphate, sodium cetyl sulphate, sodium heptadecyl sulphate, sodium octadecyl sulphate, sodium Z-pentadecyl sulphate, sodium oleyl sulphate, and any of the above named alkyl sulphates in the form of their potassium or ammonium salts. It has been found that many of the alkyl aryl sulphonate and alkyl sulphate detergents available in commerce are well suited for use in preparing the dispersions. For instance the sodium alkyl benzene sulfonate where the alkyl group contains 12 to 18 carbon atoms is suitable. This detergent is prepared by condensation of chlorinated kerosene with benzene and sulphonation or the re- Other commercially available detergents which are suitable are so-, dium decyl benzene sulphonate, sodium dodecyl benzene sulphonate, alkylated monosodium benzene sulphonate containing several alkyl groups totaling 10 carbon atoms, a mixture of sodium alkyl sulphates consisting mostly of sodium lauryl sulphate, etc. Thus we can use any alkyl aryl sulphonate or alkyl sulphate which has detergent properties.

Having thus described our invention, we claim:

1. The process comprising heating a keratin material in an essentially neutral aqueous solution containing a sulfur-containing, reductive disulphide-splitting agent and. a synthetic detergent selected from the group consisting of alkali metal salts of alkyl aryl sulphonates and of alkyl sulphates at a temperature up to about C. to disperse said keratin material in said solution.

2. The process comprising heating a. keratin material in an essentially neutral aqueous solution containing sodium bisulphite and. a synthetic detergent consisting of sodium alkyl aryl tea at a temperature up to about 100' C. to disperse said keratin'material in' said solution.

3. The process comprising heating a keratin material in an essentially neutral aqueous solution containing sodium bisuiphite and a synthetic detergent consisting 01' sodium alkyi sulphates at a temperature up to about 100 C. to disperse sa keratin material in said solution.

4. A composition of matter consisting essentially of a dispersion of a keratin material in an essentially neutral aqueous solution containing a sulfur-containing, reductive disulphide-splittin: asent and a synthetic detergent selected from thezroupcomistinzoi'slkalimetaleeltl oi alkyl aryl smphonatu and oi alkyl sulphates.

I CHASE n. .roum.

DALE K. mncnsu.

REFERENCES cI'rEn The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE PROCESS COMPRISING HEATING A KERATIN MATERIAL IN AN ESSENTIALLY NEUTRAL AQUEOUS SOLUTION CONTAINING A SULFUR-CONTAINING, REDUCTIVE DISULPHIDE-SPLITTING AGENT AND A SYNTHETIC DETERGENT SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL SALTS OF ARYL SULPHONATES AND OF ALKYL SULPHATES AT A TEMPERATURE UP TO ABOUT 100*C. TO DISPERSE SAID KERATIN MATERIAL IN SAID SOLUTION 